The general goal of the proposed studies is to develop a comprehensive model of the regulation of seasonal breeding in mammals. More specifically, I seek to identify more precisely the external cues that act alone or in concert with photoperiod to regulate seasonal breeding in male deer mice and house mice. A number of factorial experiments are proposed to study the interactive effects of four environmental factors (photoperiod, temperature, food and water availability) on reproductive neuroendocrinology. Previous studies on the control of rodent seasonal breeding have primarily focused upon the role of photoperiod (day length) influences upon breeding in animals maintained in mild laboratory temperatures with ad libitum access to food and water. However, a substantial proportion of deer mice and all house mice fail to respond to inhibitory photoperiods; these animals display seasonal breeding patterns in the field. Data from other agricultural pest species (e.g., Microtus ochrogaster, M. pinetorum) support the contention that day length cues may be unimportant in the regulation of seasonal reproduction in small opportunistic breeders. Some individual deer mice inhibit reproduction when ambient temperatures are low, whereas other mice are affected only if food intake is reduced. The proposed studies will provide data to construct a hierarchy of regulatory extrinsic cues. These studies will provide new conceptual perspectives of seasonally breeding rodents. The use of feral mice, rather than highly inbred species and the manipulation of several environmental factors instead of the traditional one or two, should allow new, ecologically relevant statements regarding the control of seasonal reproduction.